40 research outputs found
Shell model study of the isobaric chains A=50, A=51 and A=52
Shell model calculations in the full pf-shell are carried out for the A=50,
51 and 52 isobars. The most frequently used effective interactions for the
pf-shell, KB3 and FPD6 are revisited and their behaviour at the N=28 and Z=28
closures examined. Cures to their -relatively minor- defaults are proposed, and
a new mass dependent version called KB3G is released. Energy spectra,
electromagnetic transitions and moments as well as beta decay properties are
computed and compared with the experiment and with the results of the earlier
interactions. A high quality description is achieved. Other miscellaneous
topics are addressed; the Coulomb energy differences of the yrast states of the
mirror pair 51Mn-51Fe and the systematics of the magnetic moments of the N=28
isotones.Comment: 45 pages, 34 figures, Latex. Submitted for publicatio
Six-bodies calculations using the Hyperspherical Harmonics method
In this work we show results for light nuclear systems and small clusters of
helium atoms using the hyperspherical harmonics basis. We use the basis without
previous symmetrization or antisymmetrization of the state. After the
diagonalization of the Hamiltonian matrix, the eigenvectors have well defined
symmetry under particle permutation and the identification of the physical
states is possible. We show results for systems composed up to six particles.
As an example of a fermionic system, we consider a nucleon system interacting
through the Volkov potential, used many times in the literature. For the case
of bosons, we consider helium atoms interacting through a potential model which
does not present a strong repulsion at short distances. We have used an
attractive gaussian potential to reproduce the values of the dimer binding
energy, the atom-atom scattering length, and the effective range obtained with
one of the most widely used He-He interaction, the LM2M2 potential. In
addition, we include a repulsive hypercentral three-body force to reproduce the
trimer binding energy.Comment: Presented at the Sixth Workshop on the Critical Stability of Quantum
Few-Body Systems, Erice, Sicily, October 201
State Dependent Effective Interaction for the Hyperspherical Formalism
The method of effective interaction, traditionally used in the framework of
an harmonic oscillator basis, is applied to the hyperspherical formalism of
few-body nuclei (A=3-6). The separation of the hyperradial part leads to a
state dependent effective potential. Undesirable features of the harmonic
oscillator approach associated with the introduction of a spurious confining
potential are avoided. It is shown that with the present method one obtains an
enormous improvement of the convergence of the hyperspherical harmonics series
in calculating ground state properties, excitation energies and transitions to
continuum states.Comment: LaTeX, 16 pages, 8 ps figure
Particle-Number Reprojection in the Shell Model Monte Carlo Method: Application to Nuclear Level Densities
We introduce a particle-number reprojection method in the shell model Monte
Carlo that enables the calculation of observables for a series of nuclei using
a Monte Carlo sampling for a single nucleus. The method is used to calculate
nuclear level densities in the complete -shell using a good-sign
Hamiltonian. Level densities of odd-A and odd-odd nuclei are reliably extracted
despite an additional sign problem. Both the mass and the dependence of
the experimental level densities are well described without any adjustable
parameters. The single-particle level density parameter is found to vary
smoothly with mass. The odd-even staggering observed in the calculated
backshift parameter follows the experimental data more closely than do
empirical formulae.Comment: 14 pages, 4 eps figures included, RevTe
Chaotic wave functions and exponential convergence of low-lying energy eigenvalues
We suggest that low-lying eigenvalues of realistic quantum many-body
hamiltonians, given, as in the nuclear shell model, by large matrices, can be
calculated, instead of the full diagonalization, by the diagonalization of
small truncated matrices with the exponential extrapolation of the results. We
show numerical data confirming this conjecture. We argue that the exponential
convergence in an appropriate basis may be a generic feature of complicated
("chaotic") systems where the wave functions are localized in this basis.Comment: 4 figure
Parity Dependence of Nuclear Level Densities
A simple formula for the ratio of the number of odd- and even-parity states
as a function of temperature is derived. This formula is used to calculate the
ratio of level densities of opposite parities as a function of excitation
energy. We test the formula with quantum Monte Carlo shell model calculations
in the -shell. The formula describes well the transition from low
excitation energies where a single parity dominates to high excitations where
the two densities are equal.Comment: 14 pages, 4 eps figures included, RevTe
Benchmark Test Calculation of a Four-Nucleon Bound State
In the past, several efficient methods have been developed to solve the
Schroedinger equation for four-nucleon bound states accurately. These are the
Faddeev-Yakubovsky, the coupled-rearrangement-channel Gaussian-basis
variational, the stochastic variational, the hyperspherical variational, the
Green's function Monte Carlo, the no-core shell model and the effective
interaction hyperspherical harmonic methods. In this article we compare the
energy eigenvalue results and some wave function properties using the realistic
AV8' NN interaction. The results of all schemes agree very well showing the
high accuracy of our present ability to calculate the four-nucleon bound state.Comment: 17 pages, 1 figure
One maternal lineage leads the expansion of Thaumastocoris peregrinus (Hemiptera: Thaumastocoridae) in the new and old worlds.
The bronze bug, Thaumastocoris peregrinus, an Australian native insect, has become a nearly worldwide invasive pest in the last 16 years and has been causing signifcant damage to eucalypts (Myrtaceae), including Eucalyptus spp. and Corymbia spp. Its rapid expansion leads to new questions about pathways and routes that T. peregrinus used to invade other continents and countries. We used mtDNA to characterize specimens of T. peregrinus collected from 10 countries where this species has become established, including six recently invaded countries: Chile, Israel, Mexico, Paraguay, Portugal, and the United States of America. We then combined our mtDNA data with previous data available from South Africa, Australia, and Europe to construct a world mtDNA network of haplotypes. Haplotype A was the most common present in all specimens of sites sampled in the New World, Europe, and Israel, however from Australia second more frequently. Haplotype D was the most common one from native populations in Australia. Haplotype A difers from the two major haplotypes found in South Africa (D and G), confrming that at least two independent invasions occurred, one from Australia to South Africa, and the other one from Australia to South America (A). In conclusion, Haplotype A has an invasion success over many countries in the World. Additionally, analyzing data from our work and previous reports, it is possible to suggest some invasive routes of T. peregrinus to predict such events and support preventive control measures
The nuclear collective motion
Current developments in nuclear structure are discussed from a theoretical perspective. First, the progress in theoretical modeling of nuclei is reviewed. This is followed by the discussion of nuclear time scales, nuclear collective modes, and nuclear deformations. Some perspectives on nuclear structure research far from stability are given. Finally, interdisciplinary aspects of the nuclear many-body problem are outlined